Antenna



N. E. LINDENBLAD ANTENNA Filed June 27, 1942 2 Sheets-Sheet 1 May 21, 1946. N. E. LINDENBLAD 2,400,857

ANTENNA Filed June 27, 1942 2 Sheets-Sheet 2 ATTORNEY Patented ay 21, 1946 Application June 27, 1942, Serial No. 448,744

11 Claims.

The present invention relates to directive antennas'and, more particularly, to such antennas An object of the present invention is the provision of a directive antenna for use on airplanes. Another object of the present invention is the provision of an'antenna, asaforesaid, which is streamline in form and is adapted ,tobe mounted externally. on the supporting structure.

- the form of an elongated somewhat cylindrical which are particularly adaptable to useon airplanes with a minimum disturbance of the aerodynamics of the supporting structure.

tube having a streamline cross-section.

The cross-section is somewhat in the form of a tear dropiasjshown in Figure 1a. The tube is provlded with a narrow slot it! running longitudinallyalong its blunt edge. While not so shown,

the slotmay be filled in or covered with an insulating material of good dielectric characteristics.

A further object of the present invention is the provision of a compact directive antenna structure. l

Still; another object of the present invention is directive antenna'foruse on an airplane.

The foregoing objects, andothers which may appear, from the following detailed description,

are attained by the provision of an antenna in the form of a conductive tubehavinga tear drop cross-section, said tube being slotted along its blunt edge. The slot maybe covered by plastic or other insulating material having good dielectric characteristics. The tub'e is fed transversely at one point and is of ys'uch dimensions that a phase velocity within the antennais obtained whichis-of a higher-order than the velocity of ized in the plane of its transverse, cross-section. The radiation pattern obtained is of the figure 8 4 the provision of a simple, mechanically sturdy;

Any of the recently discovered plastics, such as polymerized styrene, may be used. The slotted tube is'fed by high frequency oscillatory energy from a source of such energy (not shown) by means of a transmission line TL. The transmission line TL may conveniently be of the concentric type having an outer sheath f3 and an inner conductor l4. Theouter sheath is, of course,

' electrically connected to the tube while the inner conductor I 4 is connected to a. predetermined point l5 within the tube. The point of connection I5 01 conductor'lfl to the interior of tube 10 i s'so chosenthat the impedance of the antenna is' matched to the impedance of the transmission line TL,.thus avoiding reflection of energy back into the transmission line.

In Figure l-lthe radiator H) has been indicated as having a length approximately equal to one type with the frontallobe in the direction of the blunt ed e much greater than the rear lobe. The

- pattern in the plane of the axis of the tube and of the slot is a-function of the length of the tube.

The presentinvention will. be more fully understood by reference to the-following detailed description, which is accompanied bydrawings in which Figure 1 illustrates a side View of an embodiment of the invention, while Figure 1a is a cross-section taken along lines la, la of Figure 1, and Figure 2 illustrates diagrammatically the directivity patterns obtained with the antenna of Figure 1; Figure 3 is amodificati'on of the'form of the antenna shown in FigureLwhile Figure 4 is a'further modification; and Figure 5 is a directivity pattern for the modification of Figure 4. In the following detailed description for convenience-the operation of the'invention will be considered as a transmitting antennaonly. How- "plane of thecross-section of Figure 1a.

over. it -must' be clearly understood that,-'ifdesired, the invention is equally adaptable to the reception of radiant energy waves.

In Figure 1 there is shown an antenna Ill in wavelength for the energy with which it is energize'd. Of course, the length may be made greater, light. The radiator thusradiates energy polarif desired. However, if 'the length is increased very greatly it may be desirable to energize the antenna at several points along its length in order to prevent random phase irregularities along-the length of the radiator ill. Since the velocityo'f light, energy in all sections of the cylinder. is substantially in phase if the length does not greatly exceed one wave length. The radiation from the antenna is polarized in a The radiation Pattern obtained in this plane, which is usually the horizontal plane, is of the figure 8 *"type with the rrontanob'e in the direction of the blunt edge; much greater than the rear lobe. A

- typical directivity pattern in the horizontal plane is shown by curVeIlI-of'Figure 2. The radiation i pattern in the plane'of the axis of the tube Hi {and'the slotis a function of the length of the -cylinder. For the' particular length shown in Figure1, the radiation "pattern-in this plane, the -vertical,.is shown b curve 22 of Figure '2." I This directivitypattern will be somewhat aifected by the amplitude distribution along the length of cylinder 10 which, in turmdepends on the tering the different units.

mination of the ends of the cylinder of the tube.

If the ends are closed by conductive sheets the distribution will approach the sinusoidal from end to end. The vertical directivity pattern will then be somewhat broader but more free from secondary lobes.

In Figure 3 is shown an fapplication; of the p radiator .of Figure 1 to the front of an airplane wing 30. A pair of radiators I and i0 are vertically mounted at the front edge of the wing a distance B one from the other. energized by a pair of transmission lines. such as TL of Figure 1. In order'to provide a maximum response along line M, normal to'the -edge of wing 30, the currents in radiators l0 and lllf The radiators are should be in phase, where the distance D between the radiators is a half wavelength as shown in Figure 3, and the feed lines run parallel to the edge of wing 30. There iseffectively a half wave difference in length of the'lines. -,Thus, to insure the correct energization of the radiators,-the feed linesmay be energized in a push-pull or phaseopposing relationship. Due to the half wave difference in distance that the energy is required to travel over the feed lines, when the energy arrives at the radiators I0 and i0, they will be energized in an in phase or eo-phasal relationship. If a maximum of the radiation pattern is desired along some" other line with the distance D remaining constant the phase relationship of energy applied to radiators l0, l0. may be varied by using different lengths of matched lines feed- The. phase difference must then be such that combined with space difference in the desired direction the radiation from the'various units adds-in an in phase relaon I i i A further modification of the presentinvention is shown in Figure 4 in which half sections 40, 40'

of aradiator structure such as that shown in Figure l, are mounted on a conductive sheet 45 which may, for example, be the side wall of the I fuselagefor body of an airplane.v The half sections v4Il and 40? may be spaced a distance equal to ahalfwave length along a horizontal line on the sheet 45.. The half sections are energized by means of transmission lines T111 and T10, which are energized in a push-pull or phase opposing relationship from a source of radiant energy waves (not shown),thr ough the phase inverting network 48. y The phase inverting network 48 is v constructed according; to the principles set forth in my prior Patent 2,2 38,904, granted understanding of theconstruction may be had by reference to the aforesaidmatent. I 1

The radiation pattern obtained by an antenna 7 April 22, 1941. Since this construction is not an essential part of the. present invention, other means of applying push-pull energy to transmission lines 'L'Liv and TL: beingequally adaptable thereto, the phase inverting network will not be further .describedhere, A more complete structure as shown inFigure vdis shown bycurve 1 closeness;of,;all-,parts--;ofthe antenna to conduc p; ;tive-sheet 45 ga deyiationrefleot isobtained which is of considerable magnitude. Within thepractical 'limits-ofdimensions ,oisheet 45 the deviation is. of such magnitude vthatthe antenna system 'shown-.- in Figure tmaybe used only where a 'directi'vity-pattem having amaximum'considerably off, the longitudinal:. axis of the plane is desired. .-For this..reason'the;,antenna ofFigure 4 would not ordinarily be used for the "homing type of direction finding, except as a pair directions.

mounted near the nose of theplane where the side walls converge rather sharply. i

While I have particularly shown and described several modifications of my invention, it is to be distinctly understood that my invention is not limited thereto but that improvements within the 1 scope of the invention may be madeilf Iclaim: i 1. An antenna including a section of conductive tube having a narrow longitudinal slot therein,

the circumference of said tube from one edge of .said slot to the other being of the approximate "order of half of the operating wavelength and means for soenergizing said antenna as to radiate energy polarized in a plane normal to the length of said'tube.

2. An antenna including a section of conductive tube having a narrow longitudinal slot extending from end to end thereof, the circumference of said tube from one edge of said slot to the other being of the approximate order of half of the operating wavelength and means for energizing said antenna, including a concentric transmission line having an outer sheath andan inner conductor, said outer sheath being connected to said tube at apoint diametrically'opposite to said slot and said inner conductor being connected to the inner surface of said tube at suchpoint that the impedance of said antenna, is substantially equal'to the impedance of said transmission'line.

3. An antenna including a plurality of tubes as,v

set forth in claim 2, said tubes being arranged with their slots parallel and facing in the same direction and means for energizing said'tubes in a predetermined relationship.

4. An antenna including a plurality of tubes as set forth in claim 2, said tubes being arranged side by side with their slots parallel and facing in the same direction and means for. energizing'said tubes in an in phase relationship, the spacing between said tubes being such that a maxlmum of the radiated field occurs normal to a line joining'saidtubes. 5. An antenna including a plurality of'tubes asv set forth in claim 2, said tubes being arranged one behind the other with their slots parallel and fac ing in the same direction, said tubeslbeing spaced apart a distance equal to one-half of the operating wavelength, a flat conductive sheet forming one side of both of said tubes and extending beyo d said tubes a substantial ''dits'arrcefin all 6. An-antenna including a plurality of curved 7; An antenna including'a on a conducting sheet, one longitudinaledg'eof each of said plates being in electrical contact with said sheet and the other spaced ashort dls- I tance therefrom to form an elongated slot, said slots facing in the same direction, corresponding parts of said plates being spaced apart a distance equal to a half of the, operatingiwavelength, said plates being energized in apushpull relationship from a source of high frequency energy so that a directivltypattern is formedlurallty' of 'elon-: 23 91 rved plates arranged'on'eibeside the ot having a pronounced maximum inclined from a line perpendicular to said sheet.

8. An antenna including a section of conductive tube having an arrow longitudinal slot therein, the circumference of said tube from one edge 01' said slot to the other being substantially equal to one half of the operating wavelength, said tube having an overall length substantially equal to one wavelength, and means for so coupling transducer equipment to said antenna that said antenna is operative with electromagnetic wave energy polarized in a plane normal to the length of said tube.

9. An antenna including a section of conductive tube having a narrow longitudinal slot therein, the circumference of said tube from one edge of said slot to the other being of the approximate order of one half of the operating wavelength, means for so energizing said antenna as to radiate energy polarized in a plane normal to the length of said tube, said tube having a streamlined cross section.

. 3 10. An antenna including a section of conducthe tube having a narrow, longitudinal linear slot therein, the circumference of said tube from one edge of said slot to the other being substantially equal to one half of the operating wavelength and a high frequency transmission line connected to coupled points on said tube lying in a plane normal to the longitudinal axis of said tube whereby said antenna has a maximum response to electro-magnetic wave energy polarized in a plane normal to the length of said tube.

11. An antenna including an elongated curved plate on a fiat conductive sheet, one edge of said plate being in electrical contact with said sheet and the other spaced at a distance therefrom to form an elongated slot, the width of said curved plate being substantially equal to one quarter of the operating wavelengthand means for connecting a conductor of a transmission line to said curved plate at a point substantially midway between the ends of said plate.

NILS E. LINDENBLAD. 

